The investigation is focusing on six clusters of restaurants in five states: Texas, Wisconsin, Maryland, Connecticut and Rhode Island. No illnesses have been reported in California.
Authorities are working to identify the source of the outbreak, which was described in an FDA memo as "rapid and expanding in number of cases." They are looking, specifically, at spicy tuna rolls.
FDA spokesman Curtis Allen would not confirm or elaborate on the information.
"It is too early to speculate on the cause of the outbreak," Allen said.
At least seven people have been hospitalized. No deaths have been reported.
The most common symptoms of salmonella are diarrhea, abdominal cramps and fever within eight to 72 hours of eating the contaminated food. The illness can be life-threatening in people with weakened immune systems.
The Associated Press contributed to this report.